Inflammation caused by periodontal disease, which is a typical disease of the dental region, induces jaw bone resorption. Jaw bone resorption finally promotes the loss of teeth, leading to a decline of masticatory function. So to aim the development of drug therapies that can treat and prevent periodontal disease, we examined the cyclic peptide W9, which inhibits the binding of TNF and TNF receptor. W9 peptide showed a bone resorption inhibitory action through the mechanism that inhibits the interaction of RANK / RANKL, which is important for a growth and differentiation process of osteoclasts. In addition, W9 peptide was found to possess a bone formation promoting action as shown by the detailed study of the effect of the W9 peptides on bone. Further, by exploring the DDS system of W9 peptide, the peptide was shown to be useful for the treatment of the inflammatory bone resorption disease such as the periodontal disease.